Measurement of Reference Signals with Reduced Interference

ABSTRACT

A telecommunications system is disclosed comprising a wireless switching center and plurality of base stations that are configured to transmit positioning reference signals. The base stations transmit the positioning reference signals in positioning subframe time intervals. Meanwhile, the base stations also transmit cell-specific reference signals continuously, including during the positioning subframe time intervals. In order to ensure that the wireless terminal measures those cell-specific reference signals during periods of lower interference, the base station imposes a measurement restriction on the wireless terminal, in regard to when it may measure a signal. As a result of utilizing the measurement restriction in this way, in combination with the improved interference characteristics of the positioning reference signals themselves, the ability of the wireless terminal to detect the cell-specific reference signals of more distant cells is improved. The improved signal measurements are then made available to functionalities such as location estimation.

FIELD OF THE INVENTION

The present invention relates to telecommunications in general, and,more particularly, to a technique for obtaining measurements ofreference signals with reduced interference transmitted by atelecommunication system.

BACKGROUND OF THE INVENTION

FIG. 1 depicts a diagram of the salient components of wirelesstelecommunications system 100 in accordance with the prior art. Wirelesstelecommunications system 100 comprises: wireless terminal 101, basestations 102-1, 102-2, and 102-3, wireless switching center 111,assistance server 112, location client 113, and Global PositioningSystem (“GPS”) constellation 121. Wireless telecommunications system 100provides wireless telecommunications service to all of geographic region120, in well-known fashion.

The salient advantage of wireless telecommunications over wirelinetelecommunications is the mobility that is afforded to the users. On theother hand, the salient disadvantage of wireless telecommunications liesin that fact that because the user is mobile, an interested party mightnot be able to readily ascertain the location of the user.

Such interested parties might include both the user of the wirelessterminal and remote parties. There are a variety of reasons why the userof a wireless terminal might be interested in knowing his or herlocation. For example, the user might be interested in telling a remoteparty where he or she is or might seek advice in navigation.

In addition, there are a variety of reasons why a remote party might beinterested in knowing the location of the user. For example, therecipient of an E 9-1-1 emergency call from the wireless terminal mightbe interested in knowing the location of the wireless terminal so thatemergency services vehicles can be dispatched to that location.

There are many techniques in the prior art for estimating the locationof a wireless terminal. In accordance with some techniques, the locationof a wireless terminal is estimated, at least in part, from signalmeasurements that are reported by the wireless terminal. The reportedmeasurements are of signals measured by the wireless terminal that aretransmitted by one or more base stations and, in some cases, by GPSsatellites.

Wireless terminal 101 reports measurements to telecommunications system100, which measurements can then be used for location estimationpurposes. Independent of location estimation, however, terminal 101monitors the strength of signals transmitted by multiple neighboringbase stations, such as base station 102-1 through 102-3, in order toensure that the terminal is always communicating with the base stationthat provides the strongest signal. If, at some point, another basestation is found to provide a stronger signal, the call that involvesthe user of terminal 101 might need to be handed over to the other basestation. Terminal 101 can then ask the system to initiate a handover.This technique is known as a “mobile-assisted handover” (MAHO).

In addition to other signals that provide connectivity for the wirelessterminals, each of base station 102-1 through 102-3 also transmits asignal that is designed to be relatively tolerant of interference. Suchsignals are known by various names such as “pilots” in systems that arebased on code division multiple access (CDMA), or “cell-specificreference signals” (CRS) in systems that are based on 3^(rd) GenerationPartnership Project (3GPP) Long-Term Evolution (LTE). Thesereference-type signals can achieve greater interference tolerancebecause they carry very little information, essentially carrying theidentity of the originating cell only.

The cell-specific reference signals enhance the detectability of signalsfrom neighboring cells and make MAHO possible.

SUMMARY OF THE INVENTION

There are system functionalities other than mobile-assisted handover(MAHO), such as some location estimation techniques, that benefit fromthe ability to accurately detect signals from neighboring cells and,specifically, from the ability to estimate parameters of such signals.The problem with relying solely on cell-specific reference signals fornon-MAHO functionalities, however, is that these reference signals weredesigned for detection by a wireless terminal primarily when the signalis transmitted by the base station of the serving cell of the wirelessterminal or by a base station of a cell that is adjacent to the servingcell. Consequently, cell-specific reference signals that are transmittedfrom base stations that are further away from the wireless terminal canbe difficult to detect and, hence, often unreliable for use in at leastsome non-MAHO functionalities in the prior art. Location estimation thatrelies on measurements by a wireless terminal is one such functionality.

In addition to providing for the transmission of cell-specific referencesignals, the Long-Term Evolution (LTE) standard also provides acapability for estimating the location of wireless terminals, based on atechnique referred to as “observed time difference of arrival” (OTDOA).OTDOA requires relative timing measurements to be made by the terminal.To support this capability, LTE requires that each base stationtransmit, at regular intervals, a signal known as a “positioningreference signal” (PRS). A PRS is designed to enable precise estimationof its time of arrival when received by a wireless terminal. In atypical use of these signals, a wireless terminal compares propagationtime differences of signals from multiple base stations to estimate itsown location.

The present invention enables a wireless terminal to measure referencesignals with improved interference characteristics over at least sometechniques in the prior art. The present invention is based on theobservation by its inventors that the positioning reference signals usedin the LTE standard, though optimized for precise estimation of time ofarrival, also happen to have good characteristics for interferencemitigation. In other words, the interference caused by positioningreference signals is less than the interference caused by other signalsin the LTE standard, and it is easier to mitigate by using well-knownand commonly used interference-mitigation techniques.

In accordance with the illustrative embodiment of the present invention,a telecommunications system comprises a wireless switching center (WSC)and plurality of base stations that are configured to transmitpositioning reference signals. The base stations transmit thepositioning reference signals in positioning subframe time intervals.Meanwhile, the base stations also transmit cell-specific referencesignals continuously, including during the positioning subframe timeintervals. In order to ensure that the wireless terminal measures thosecell-specific reference signals during periods of lower interference,the base station advantageously imposes a measurement restriction on thewireless terminal, in regard to when it may measure a signal. Such ameasurement restriction mechanism is available in LTE, as the inventorshave observed, although it was previously used for other applications.As an example, the measurement restriction capability was previouslyapplied to supporting femtocells that were deployed in an area where anLTE-based cellular system provides macrocellular service in the samespectrum. To avoid disruption of the macrocellular system, thefemtocells were directed to transmit minimal amounts of radio signal incertain designated time intervals known as “almost blank subframes”(ABS). The macrocellular system would direct wireless terminals toattempt to detect cell-specific reference signals only in the ABS timeintervals. The advantage of doing so was that, during ABS intervals,interference from femtocells was minimized.

In contrast to the traditional application of the measurementrestriction mechanism, such as for femtocell management, the basestation of the illustrative embodiment directs the wireless terminal todetect the cell-specific reference signals only in the positioningsubframe time intervals. As a result of utilizing the measurementrestriction in this way, in combination with the improved interferencecharacteristics of the positioning reference signals themselves, theability of the wireless terminal to detect the cell-specific referencesignals of more distant cells is advantageously improved. This has theadded benefit of making available improved measurements tofunctionalities such as location estimation, thereby improving theirperformance as well.

In some embodiments, the base station also transmits a measurementdirective to the wireless terminal, in order to explicitly command theterminal to measure the reference signals and to return thecorresponding measurement results. In some embodiments, a locationestimation system can command the base station to transmit thedirective, or can use the measurement results in a location estimationprocedure, or both.

Although the telecommunications system of the illustrative embodimentutilizes the 3GPP LTE set of standards, it will be clear to thoseskilled in the art, after reading this specification, how to make anduse embodiments of the present invention in which other standards areutilized, in addition to or instead of LTE. Such standards include, butare not limited to, Universal Mobile Telecommunications System “UMTS”,Global System Mobile “GSM,” CDMA-2000, IS-136 TDMA, IS-95 CDMA, 3GWideband CDMA, IEEE 802.11 WiFi, 802.16 WiMax, and Bluetooth. In suchembodiments reference signals, in addition to or instead ofcell-specific reference signals and positioning reference signals, maybe used, as those who are skilled in the art will appreciate afterreading this specification.

The telecommunications system of the illustrative embodiment featuresmeasurement of cell-specific reference signals during the positioningsubframe time intervals, in order to improve location estimationperformance. It will be clear, however, to those skilled in the art,after reading this specification, how to make and use embodiments of thepresent invention in order to improve the performance of otherfunctionalities that utilize measurements made by a wireless terminal.

An illustrative embodiment of the present invention comprises:transmitting, by a base station, a measurement directive to a wirelessterminal to measure one or more cell-specific reference signals, whereina measurement restriction transmitted to the wireless terminal indicatesdesignated time intervals of one or more positioning subframes in whichpositioning reference signals are transmitted by one or more basestations, and wherein the measurement restriction imposes a restrictionon the wireless terminal to measure the one or more cell-specificreference signals coincident with the designated time intervals; andreceiving, by the base station, a measurement result from the wirelessterminal in response to the measurement directive being transmitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a diagram of the salient components of wirelesstelecommunications system 100 in accordance with the prior art.

FIG. 2 depicts a diagram of the salient components of wirelesstelecommunications system 200 in accordance with the illustrativeembodiment of the present invention.

FIG. 3 depicts a block diagram of the salient components of base station202, as shown in FIG. 2, in accordance with the illustrative embodiment.

FIG. 4 depicts a block diagram of the salient components of locationserver 214, as shown in FIG. 2, in accordance with the illustrativeembodiment.

FIG. 5 depicts a flowchart of the salient processes performed inaccordance with the illustrative embodiment of the present invention.

FIG. 6 depicts a flowchart of the salient sub-processes of process 501as shown in FIG. 5, performed in accordance with the illustrativeembodiment of the present invention.

FIG. 7 depicts a flowchart of the salient sub-processes of process 502as shown in FIG. 5, performed in accordance with the illustrativeembodiment of the present invention.

FIG. 8 depicts a flowchart of the salient sub-processes of process 504as shown in FIG. 5, performed in accordance with the illustrativeembodiment of the present invention.

DETAILED DESCRIPTION

For the purposes of this specification, the following terms and theirinflected forms are defined as follows:

-   -   The term “location” is defined as a one-dimensional point, a        two-dimensional area, or a three-dimensional volume.    -   The term “cell-specific reference signal” (CRS) is defined in        “3^(rd) Generation Partnership Project; Technical Specification        Group Radio Access Network; Evolved Universal Terrestrial Radio        Access (E-UTRA); Physical Channels and Modulation (Release 9),        V9.1.0 (2010-03),” incorporated herein by reference and referred        to hereinafter as “3GPP TS 36.211.” A cell-specific reference        signal is analogous to a CDMA pilot signal. The cell-specific        reference signal is transmitted from each physical antenna port        at a base station and is used by a wireless terminal for        demodulation and measurement purposes.    -   The term “positioning reference signal” (PRS) is also defined in        3GPP TS 36.211. It is made up of one or more downlink symbols in        a time and frequency grid that are known to a signaling base        station and a decoding wireless terminal. Although not limited        in its application, PRS can be used for estimation of the        position of a wireless terminal for localization services,        having been specified initially for support of the observed time        difference of arrival (OTDOA) method. The terms “position        reference signal” and “positioning signal” are used        interchangeably with the term “positioning reference signal.”        Positioning referencing signals are also referred to as “idle        periods in the downlink (IPDL) reference signals or “enhanced        IPDL (e-IPDL) reference signals.”    -   The term “positioning subframe” is defined as the conveyance        mechanism of a positioning reference signal.

FIG. 2 depicts a diagram of the salient components of wirelesstelecommunications system 200 in accordance with the illustrativeembodiment of the present invention. Wireless telecommunications system200 comprises: wireless terminal 201, base stations 202-1, 202-2, and202-3, wireless switching center 211, assistance server 212, locationclient 213, location server 214, and GPS constellation 221, which areinterrelated as shown. The illustrative embodiment provides wirelesstelecommunications service to all of geographic region 220, inwell-known fashion, estimates the location of wireless terminal 201within geographic region 220, and uses that estimate in a location-basedapplication.

In accordance with the illustrative embodiment, wirelesstelecommunications service is provided to wireless terminal 201 inaccordance with the Long Term Evolution set of standards, which iscommonly known as “LTE.” After reading this disclosure, however, it willbe clear to those skilled in the art how to make and use alternativeembodiments of the present invention that operate in accordance with oneor more other air-interface standards (e.g., Universal MobileTelecommunications System “UMTS”, Global System Mobile “GSM,” CDMA-2000,IS-136 TDMA, IS-95 CDMA, 3G Wideband CDMA, IEEE 802.11 WiFi, 802.16WiMax, Bluetooth, etc.) in one or more frequency bands.

Wireless terminal 201 comprises the hardware and software necessary tobe LTE-compliant and to perform the processes described below and in theaccompanying figures. For example and without limitation, wirelessterminal 201 is capable of:

-   -   i. measuring one or more traits of one of more electromagnetic        signals and of reporting the measurements to location server        214, and    -   ii. transmitting one or more signals and of reporting the        transmission parameters of the signals to location server 214,        and    -   iii. receiving GPS assistance data from assistance server 212 to        assist it in acquiring and processing GPS ranging signals.        As is well known to those skilled in the art, a wireless        terminal is also commonly referred to by a variety of        alternative names such as a wireless transmit/receive unit        (WTRU), a user equipment (UE), a mobile station, a fixed or        mobile subscriber unit, a pager, a cellular telephone, a        personal digital assistant (PDA), a computer, or any other type        of device capable of operating in a wireless environment.

Wireless terminal 201 is mobile and can be at any location withingeographic region 220. Although wireless telecommunications system 200as depicted comprises only one wireless terminal, it will be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments of the present invention that comprise anynumber of wireless terminals.

Base stations 202-1, 202-2, and 202-3 communicate with wirelessswitching center 211 and with wireless terminal 201 via radio inwell-known fashion. As is well known to those skilled in the art, basestations are also commonly referred to by a variety of alternative namessuch as access points, nodes (e.g., Node-B, eNode-B, etc.), networkinterfaces, etc. Base stations 202-1, 202-2, and 202-3 also communicatewith one another, in some embodiments. Direct interfaces between thebase stations are not depicted; however, it will be clear to thoseskilled in the art, after reading this disclosure, how to make and usealternative embodiments of the present invention in which base stationscommunicate directly with each other, such as through an X2 interface asis known in the art.

Although the illustrative embodiment comprises three base stations, itwill be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention that comprise any number of base stations.

In accordance with the illustrative embodiment of the present invention,base stations 202-1, 202-2, and 202-3 are terrestrial, immobile, andwithin geographic region 220. It will be clear to those skilled in theart, after reading this disclosure, how to make and use alternativeembodiments of the present invention in which some or all of the basestations are airborne, marine-based, or space-based, regardless ofwhether or not they are moving relative to the Earth's surface, andregardless of whether or not they are within geographic region 220.

Wireless switching center 211 comprises a switch that orchestrates theprovisioning of telecommunications service to wireless terminal 201 andthe flow of information to and from location server 214, as describedbelow and in the accompanying figures. As is well known to those skilledin the art, wireless switching centers are also commonly referred to byother names such as mobility management entities (MME), mobile switchingcenters, mobile telephone switching offices (MTSO), routers, etc.

Although the illustrative embodiment comprises one wireless switchingcenter, it will be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention that comprise any number of wireless switching centers.

In accordance with the illustrative embodiment, all of the base stationsservicing wireless terminal 201 are associated with wireless switchingcenter 211. It will be clear to those skilled in the art, after readingthis disclosure, how to make and use alternative embodiments of thepresent invention in which any number of base stations are associatedwith any number of wireless switching centers.

Assistance server 212 comprises hardware and software that is capable ofperforming the processes described below and in the accompanyingfigures. In general, assistance server 212 generates GPS assistance datafor wireless terminal 201 to aid wireless terminal 201 in acquiring andprocessing GPS ranging signals from GPS constellation 221. In accordancewith the illustrative embodiment, assistance server 212 is a separatephysical entity from location server 214; however, it will be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments of the present invention in which assistanceserver 212 and location server 214 share hardware, software, or both.

Location client 213 comprises hardware and software that use theestimate of the location of wireless terminal 201—provided by locationserver 214—in a location-based application, as described below and inthe accompanying figures.

Location server 214 comprises hardware and software that generate one ormore estimates of the location of wireless terminal 201 as describedbelow and in the accompanying figures. It will be clear to those skilledin the art, after reading this disclosure, how to make and use locationserver 214. Furthermore, although location server 214 is depicted inFIG. 2 as physically distinct from wireless switching center 211, itwill be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention in which location server 214 is wholly or partially integratedwith wireless switching center 211.

In accordance with the illustrative embodiment, location server 214communicates with wireless switching center 211, assistance server 212,and location client 213 via a local area network; however it will beclear to those skilled in the art, after reading this disclosure, how tomake and use alternative embodiments of the present invention in whichlocation server 214 communicates with one or more of these entities viaa different network such as, for example and without limitation, theInternet, the Public Switched Telephone Network (PSTN), etc.

In accordance with the illustrative embodiment, wireless switchingcenter 211, assistance server 212, location client 213, and locationserver 214 are outside of geographic region 220. It will be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments of the present invention in which some orall of wireless switching center 211, assistance server 212, locationclient 213, and location server 214 are instead within geographic region220.

FIG. 3 depicts a block diagram of the salient components of base station202 (i.e., base station 202-1, 202-2, or 202-3) in accordance with theillustrative embodiment. Base station 202 comprises: processor 301,memory 302, radio-frequency (RF) transceiver 303, and networktransceiver 304, which are interconnected as shown.

Processor 301 is a general-purpose processor that is capable ofexecuting operating system 311 and application software 312, includingthe tasks described in detail below and in the accompanying figures. Itwill be clear to those skilled in the art how to make and use processor301.

Memory 302 is a non-volatile memory that stores:

i. operating system 311, and

ii. application software 312.

It will be clear to those skilled in the art how to make and use memory302.

RF transceiver 303 enables base station 202 to transmit and receiveinformation to and from one or more wireless terminals, includingwireless terminal 201. It will be clear to those skilled in the art howto make and use RF transceiver 303.

Network transceiver 304 enables base station 202 to transmit informationto and receive information from location server 214 via wirelessswitching center 211. It will be clear to those skilled in the art howto make and use network transceiver 304.

FIG. 4 depicts a block diagram of the salient components of locationserver 214 in accordance with the illustrative embodiment. Locationserver 214 comprises: processor 401, memory 402, and local-area networktransceiver 403, which are interconnected as shown.

Processor 401 is a general-purpose processor that is capable ofexecuting operating system 411 and application software 412, and ofpopulating, amending, using, and managing Location-Trait Database 413and Trait-Correction Database 414, as described in detail below and inthe accompanying figures. It will be clear to those skilled in the arthow to make and use processor 401.

Memory 402 is a non-volatile memory that stores:

i. operating system 411, and

ii. application software 412, and

iii. Location-Trait Database 413, and

iv. Trait-Correction Database 414.

It will be clear to those skilled in the art how to make and use memory402.

Transceiver 403 enables location server 214 to transmit and receiveinformation to and from wireless switching center 211, assistance server212, and location client 213. In addition, transceiver 403 enableslocation server 214 to transmit information to and receive informationfrom wireless terminal 201 and base stations 202-1 through 202-3 viawireless switching center 211. It will be clear to those skilled in theart how to make and use transceiver 403.

FIG. 5 depicts a flow diagram of the salient processes performed inaccordance with the illustrative embodiment of the present invention.

In accordance with process 501, location server 214 performs locationestimation on wireless terminal 201 on an on-going basis. The details ofperforming location estimation are described below and with respect toFIG. 6.

In accordance with process 502, base station 202 configures thetransmission of reference signals, the details of which are describedbelow and with respect to FIG. 7.

In accordance with process 503, wireless terminal 201 engages with basestation 202 in a network access procedure, in well-known fashion. Insome embodiments, terminal 201 performs an enhanced, random accesschannel (RACH) procedure, during which the terminal indicates itsinterference status or provides additional interference information tobase station 202, or both, in order to improve interferencecoordination.

In accordance with process 504, base station 202 exchanges referencesignal-related information with wireless terminal 201 on an on-goingbasis. Concurrently, location server 214 exchanges measurement-relatedmessages with base station 202 (via wireless switching center 211). Thedetails of performing these exchanges are described below and withrespect to FIG. 8. In brief, base station 202 transmits measurementrestriction 505 of the designated time intervals of one or morepositioning subframes in which positioning reference signals aretransmitted.

Asynchronously with respect to the transmission of measurementrestriction 505, base station 202 receives measurement request 506 fromlocation server 214 and, in response, transmits measurement directive507 to terminal 201. Base station 202 is also capable of receivingmeasurement result 508 from terminal 201 and, in response, oftransmitting measurement result 509 to server 214.

FIG. 6 depicts a flowchart of the salient sub-processes of process 501,performed in accordance with the illustrative embodiment of the presentinvention. The flowchart provides an overview of a location estimationtechnique that uses measurements received from wireless terminal 201.The details of the illustrative location estimation technique aredescribed in U.S. Pat. No. 7,257,414, which is incorporated herein byreference. Although FIG. 6 features a particular location estimationtechnique, it will be clear to those skilled in the art, after readingthis specification, how to make and use embodiments of the presentinvention that interact with a different location estimation technique.

In accordance with process 601, location server 214 buildsLocation-Trait Database 413. For the purposes of this specification, the“Location-Trait Database” is defined as a database that maps each of aplurality of locations to one or more expected traits associated with awireless terminal at that location.

In accordance with process 602, server 214 builds Trait-CorrectionDatabase 414. For the purposes of this specification, the“Trait-Correction Database” is defined as a database that indicates howthe measurement of traits can be adjusted to compensate for systemicmeasurement errors.

In accordance with process 603, server 214 estimates the location ofwireless terminal 201 based on location-trait database 413,trait-correction database 414, and a variety of traits that vary basedon the location of wireless terminal 201. When needed, server 214transmits measurement requests (e.g., request 506, etc.) to base station202, in order to obtain a measurement result from wireless terminal 201.In some embodiments, in response to receiving a measurement result(e.g., result 509, etc.), server 214 uses the measurement result forgenerating an estimate of the location of wireless terminal 201.

In some embodiments server 214 uses the measurement result for any of avariety of location estimation techniques, in order to generate thelocation estimate. For example and without limitation, server 214 cangenerate the estimate by using—or refraining from using—patternmatching, assisted GPS, observed time difference of arrival (OTDOA)measurements, enhanced cell identifier (ECID) positioning, and so on.

In accordance with process 604, the estimate of the location of wirelessterminal 201 is used in a location-based application, such as andwithout limitation, E 9-1-1 service.

In accordance with process 605, Location-Trait Database 413 andTrait-Correction Database 414 are maintained so that their contents areaccurate, up-to-date and complete.

FIG. 7 depicts a flowchart of the salient sub-processes of process 502,performed in accordance with the illustrative embodiment of the presentinvention. Although base station 202 performs the processes asdescribed, it will be clear to those skilled in the art, after readingthis disclosure, how to make and use alternative embodiments of thepresent invention in which wireless switching center 211 performs someor all of the processes.

In accordance with process 701, base station 202 configures one or morebase stations to transmit cell-specific reference signals, in well-knownfashion.

In accordance with process 702, base station 202 configures one or basestations to transmit positioning reference signals in positioningsubframes, in well-known fashion. Base station 202 configures the basestations such that cell-specific reference signals are also transmittedduring the time intervals in which the positioning subframes aretransmitted.

In accordance with process 703, base station 202 determines thedesignated time intervals in which the positioning subframes aretransmitted, in well-known fashion. In some embodiments, base station202 also bases the designated time intervals on when almost blanksubframes (ABS) are transmitted by one or more neighbor cells. Forexample and without limitation, a neighbor cell transmitting suchsubframes can be a femtocell, as discussed below and with respect toFIG. 8.

FIG. 8 depicts a flowchart of the salient sub-processes of process 504,performed in accordance with the illustrative embodiment of the presentinvention.

In accordance with process 801, base station 202 transmits measurementrestriction 505 to wireless terminal 201, which restriction indicatesthe designated time intervals ascertained at process 703. Thetransmitted measurement restriction imposes a restriction on thewireless terminal to measure one or more cell-specific reference signalscoincident with the designated time intervals. This type of restrictionis, in fact, referred to in the art as “measurement restriction.”

In accordance with the illustrative embodiment, a measurementrestriction indicates which of 40 subframes a wireless terminal canmeasure. In accordance with the LTE standard, 40 subframes span 40milliseconds of time, but PRS subframes may be transmitted no morefrequently than once every 160 milliseconds. Thus, base station 202 isable to specify to wireless terminal 201 that only every fourthmeasurement will be during a PRS subframe, albeit during all PRSsubframes while the measurement restriction is in effect. It will,however, be clear to those skilled in the art, after reading thisspecification, how to configure base station 202 to instead impose anarrower restriction, in that wireless terminal 201 measures one or morecell-specific reference signals only during the designated timeintervals.

In the prior art, the measurement restriction capability has beenapplied to supporting femtocells that are deployed in an area where anLTE-based cellular system provides macrocellular service in the samespectrum. To avoid disruption of the macrocellular system, thefemtocells are directed to transmit minimal amounts of radio signal incertain designated time intervals known as “almost blank subframes”(ABS). The macrocellular system directs wireless terminals to attempt todetect cell-specific reference Signals only in the ABS time intervals.The advantage of doing so is that, during ABS intervals, interferencefrom femtocells is minimized. In contrast, and in accordance with theillustrative embodiment, telecommunications system 200, specificallybase station 202, directs wireless terminal 201 to detect thecell-specific reference signals only in the positioning subframe timeintervals. In some alternative embodiments, however, system 200 mightdirect terminal 201 to detect the cell-specific reference signals inadditional time intervals (e.g. in at least some ABS time intervals,etc.).

Base station 202 transmits measurement restriction 505 over a broadcastchannel (BCH), in well-known fashion, wherein the measurementrestriction is in the form of a mask. In some embodiments, station 202transmits the measurement restriction to terminal 201 in some othersignaling message. In some other embodiments, station 202 transmits themeasurement restriction based on a location estimation process, such asthe one described above and with respect to FIG. 6.

In some embodiments, the transmitting of measurement restriction 505 isbased on a predetermined characteristic of wireless terminal 201. Insome other embodiments, the transmitting of the measurement restrictionis based on the location of the wireless terminal or on an estimate ofsaid location. In still some other embodiments, the transmitting of themeasurement restriction is based on a measured level of interference(e.g., measured by one or more wireless terminals, measured by one ormore base stations, etc.).

In accordance with process 802, base station 202 transmits measurementdirective 507 to wireless terminal 201. Directive 507, in someembodiments, identifies specific signal sources to measure.

In some embodiments, the transmitting of measurement directive 507 isbased on a predetermined characteristic of wireless terminal 201. Insome other embodiments, the transmitting of the measurement directive isbased on the location of the wireless terminal or on an estimate of saidlocation. In still some other embodiments, the transmitting of themeasurement directive is based on a measured level of interference (e.g.measured by one or more wireless terminals, measured by one or more basestations, etc.).

In response to receiving directive 507, wireless terminal 201 performsmeasurements on one or more cell-specific reference signals and providesone or more measurement results (e.g., result 508, etc.) back to basestation 202. The wireless terminal might perform the measurements usingthe same techniques that it would normally use to perform thosemeasurements.

In some alternative embodiments, wireless terminal 201 might perform themeasurements using techniques that take advantage of the specificcharacteristics of the positioning reference signals to further improveand enhance the quality of the measurements. For example, thepositioning reference signals might exhibit mutual orthogonality, whichis a desirable characteristic in signals that are optimized for OTDOA.It is well known in the art how to take advantage of orthogonality toreduce interference caused by orthogonal signals.

In accordance with process 803, base station 202 receives measurementresult 508 from wireless terminal 201. In response, station 202 forwardsthe result to location server 214 via message 509.

In accordance with process 504, base station 202 is capable of repeatingsome or all of processes 801 through 803, either in response to one ormore messages received from location server 214 and/or wireless terminal201, or autonomously, or both.

It is to be understood that the disclosure teaches just one example ofthe illustrative embodiment and that many variations of the inventioncan easily be devised by those skilled in the art after reading thisdisclosure and that the scope of the present invention is to bedetermined by the following claims.

What is claimed is:
 1. A method comprising: transmitting, by a basestation, a measurement directive to a wireless terminal to measure oneor more cell-specific reference signals, wherein a measurementrestriction transmitted to the wireless terminal indicates designatedtime intervals of one or more positioning subframes in which positioningreference signals are transmitted by one or more base stations, andwherein the measurement restriction imposes a restriction on thewireless terminal to measure the one or more cell-specific referencesignals coincident with the designated time intervals; and receiving, bythe base station, a measurement result from the wireless terminal inresponse to the measurement directive being transmitted.
 2. The methodof claim 1 further comprising configuring the one or more base stationsto transmit the positioning subframes.
 3. The method of claim 2 furthercomprising: determining the designated time intervals during which theone or more positioning subframes are transmitted; and transmitting themeasurement restriction, wherein the measurement restriction is based onthe determining of the designated time intervals.
 4. The method of claim1 wherein the transmitting of the measurement directive is based on agiven location estimation process.
 5. The method of claim 4 furthercomprising generating an estimate of the location of the wirelessterminal, wherein the estimate is based on the measurement result andthe location estimation process.
 6. The method of claim 5 wherein theestimate is obtained without using observed time difference of arrival(OTDOA) measurements.
 7. The method of claim 5 wherein the estimate isobtained using enhanced cell identifier (ECID) positioning.
 8. Themethod of claim 1 wherein the transmitting of the measurement directiveis based on a predetermined characteristic of the wireless terminal. 9.The method of claim 1 wherein the transmitting of the measurementdirective is based on an estimate of the location of the wirelessterminal.
 10. A method comprising: determining, by a telecommunicationssystem comprising one or more base stations, designated time intervalsof one or more positioning subframes in which one or more positioningreference signals are to be transmitted by the one or more basestations; transmitting, by the telecommunications system to a wirelessterminal, a measurement restriction that indicates the designated timeintervals, wherein the measurement restriction imposes a restriction onthe wireless terminal to measure one or more cell-specific referencesignals coincident with the designated time intervals; and receiving ameasurement result from the wireless terminal of the one or morecell-specific reference signals.
 11. The method of claim 10 furthercomprising transmitting a measurement directive to the wireless terminalto measure the one or more cell-specific reference signals, wherein themeasurement result is received in response to the measurement directivebeing transmitted.
 12. The method of claim 10 wherein the designatedtime intervals are also based on when one or more almost blank subframesare transmitted by a neighbor cell.
 13. The method of claim 12 whereinthe neighbor cell is a femtocell.
 14. The method of claim 10 wherein thetransmitting of the measurement restriction is based on a given locationestimation process.
 15. The method of claim 14 further comprisinggenerating an estimate of the location of the wireless terminal, whereinthe estimate is based on the measurement result and the locationestimation process.
 16. The method of claim 15 wherein the estimate isobtained without using observed time difference of arrival (OTDOA)measurements.
 17. The method of claim 15 wherein the estimate isobtained using enhanced cell identifier (ECID) positioning.
 18. Themethod of claim 10 wherein the transmitting of the measurementrestriction is based on a predetermined characteristic of the wirelessterminal.
 19. The method of claim 10 wherein the transmitting of themeasurement restriction is based on an estimate of the location of thewireless terminal.
 20. The method of claim 10 wherein the transmittingof the measurement restriction is based on a measured level ofinterference.
 21. A method comprising: determining, by atelecommunications system comprising one or more base stations,designated time intervals of one or more positioning subframes in whichone or more positioning reference signals are to be transmitted by theone or more base stations; transmitting, by the telecommunicationssystem to a wireless terminal, a measurement restriction that indicatesthe designated time intervals, wherein the measurement restrictionimposes a restriction on the wireless terminal to measure one or morecell-specific reference signals coincident with the designated timeintervals, and wherein the transmitting of the measurement restrictionis based on a given location estimation process; receiving a measurementresult from the wireless terminal of the one or more cell-specificreference signals; and generating an estimate of the location of thewireless terminal, wherein the estimate is based on the measurementresult and the location estimation process.
 22. The method of claim 21wherein the estimate is obtained without using observed time differenceof arrival (OTDOA) measurements.
 23. The method of claim 21 wherein theestimate is obtained using enhanced cell identifier (ECID) positioning.24. The method of claim 21 further comprising transmitting a measurementdirective to the wireless terminal to measure the one or morecell-specific reference signals, wherein the transmitting of themeasurement directive is based on the location estimation process, andwherein the measurement result is received in response to themeasurement directive being transmitted.
 25. The method of claim 24wherein the transmitting of the measurement directive is also based on aprior location estimate of the wireless terminal.
 26. An apparatuscomprising: a transmitter for transmitting a measurement directive to awireless terminal to measure one or more cell-specific referencesignals, wherein a measurement restriction transmitted to the wirelessterminal indicates designated time intervals of one or more positioningsubframes in which positioning reference signals are transmitted by oneor more base stations, and wherein the measurement restriction imposes arestriction on the wireless terminal to measure the one or morecell-specific reference signals coincident with the designated timeintervals; and a receiver for receiving a measurement result from thewireless terminal in response to the measurement directive beingtransmitted.
 27. The apparatus of claim 26 further comprising atelecommunications system for configuring the one or more base stationsto transmit the positioning subframes.
 28. The apparatus of claim 27further comprising: a processor for determining the designated timeintervals during which the one or more positioning subframes aretransmitted; wherein the transmitter is also for transmitting themeasurement restriction, wherein the measurement restriction is based onthe determining of the designated time intervals.
 29. The apparatus ofclaim 26 wherein the transmitting of the measurement directive is basedon a given location estimation process.
 30. The apparatus of claim 29further comprising a location server for generating an estimate of thelocation of the wireless terminal, wherein the estimate is based on themeasurement result and the location estimation process.
 31. Theapparatus of claim 30 wherein the estimate is obtained without usingobserved time difference of arrival (OTDOA) measurements.
 32. Theapparatus of claim 30 wherein the estimate is obtained using enhancedcell identifier (ECID) positioning.
 33. The apparatus of claim 26wherein the transmitting of the measurement directive is based on apredetermined characteristic of the wireless terminal.
 34. The apparatusof claim 26 wherein the transmitting of the measurement directive isbased on an estimate of the location of the wireless terminal.
 35. Anapparatus comprising: a processor for determining designated timeintervals of one or more positioning subframes in which one or morepositioning reference signals are to be transmitted by one or more basestations in a telecommunications system; a transmitter for transmitting,to a wireless terminal, a measurement restriction that indicates thedesignated time intervals, wherein the measurement restriction imposes arestriction on the wireless terminal to measure one or morecell-specific reference signals coincident with the designated timeintervals; and a receiver for receiving a measurement result from thewireless terminal of the one or more cell-specific reference signals.36. The apparatus of claim 35 wherein the transmitter is also fortransmitting a measurement directive to the wireless terminal to measurethe one or more cell-specific reference signals, wherein the measurementresult is received in response to the measurement directive beingtransmitted.
 37. The apparatus of claim 35 wherein the designated timeintervals are also based on when one or more almost blank subframes aretransmitted by a neighbor cell.
 38. The apparatus of claim 37 whereinthe neighbor cell is a femtocell.
 39. The apparatus of claim 35 whereinthe transmitting of the measurement restriction is based on a givenlocation estimation process.
 40. The apparatus of claim 39 furthercomprising a location server for generating an estimate of the locationof the wireless terminal, wherein the estimate is based on themeasurement result and the location estimation process.
 41. Theapparatus of claim 40 wherein the estimate is obtained without usingobserved time difference of arrival (OTDOA) measurements.
 42. Theapparatus of claim 40 wherein the estimate is obtained using enhancedcell identifier (ECID) positioning.
 43. The apparatus of claim 35wherein the transmitting of the measurement restriction is based on apredetermined characteristic of the wireless terminal.
 44. The apparatusof claim 35 wherein the transmitting of the measurement restriction isbased on an estimate of the location of the wireless terminal.
 45. Theapparatus of claim 35 wherein the transmitting of the measurementrestriction is based on a measured level of interference.
 46. An systemcomprising: a base station for: (i) determining designated timeintervals of one or more positioning subframes in which one or morepositioning reference signals are to be transmitted by one or more basestations in a telecommunications system, (ii) transmitting, to awireless terminal, a measurement restriction that indicates thedesignated time intervals, wherein the measurement restriction imposes arestriction on the wireless terminal to measure one or morecell-specific reference signals coincident with the designated timeintervals, and wherein the transmitting of the measurement restrictionis based on a given location estimation process, and (iii) receiving ameasurement result from the wireless terminal of the one or morecell-specific reference signals; and a location server for generating anestimate of the location of the wireless terminal, wherein the estimateis based on the measurement result and the location estimation process.47. The system of claim 46 wherein the estimate is obtained withoutusing observed time difference of arrival (OTDOA) measurements.
 48. Thesystem of claim 46 wherein the estimate is obtained using enhanced cellidentifier (ECID) positioning.
 49. The system of claim 46 wherein thebase station is also for transmitting a measurement directive to thewireless terminal to measure the one or more cell-specific referencesignals, wherein the transmitting of the measurement directive is basedon the location estimation process, and wherein the measurement resultis received in response to the measurement directive being transmitted.50. The system of claim 49 wherein the transmitting of the measurementdirective is also based on a prior location estimate of the wirelessterminal.